Three-piece, wound golf balls with balata covers are preferred by most expert golfers. These balls provide a combination of distance, high spin rate, and control that is not available with other types of golf balls. However, balata is easily damaged in normal play, and, thus, lacks the durability required by the average golfer.
In contrast, amateur golfers typically prefer a solid, two-piece ball with an ionomer cover, which provides a combination of distance and durability. Because of the hard ionomer cover, these balls are almost impossible to cut, but they also have a very hard "feel", which many golfers find unacceptable, and a lower spin rate, making these balls more difficult to draw or fade. The differences in the spin rate can be attributed to the differences in the composition and construction of both the cover and the core.
Many attempts have been made to produce a golf ball with the control and feel of a wound balata ball and the durability of a solid, two-piece ball, but none have succeeded totally. For example, U.S. Pat. No. 4,274,637 to Molitor discloses two- and three-piece golf balls having covers completely or partially formed from a cellular polymeric material to improve backspin, but does not provide any examples that compare the spin rates of the disclosed golf balls with those of prior art balls.
U.S. Pat. No. 5,002,281 to Nakahara et al. discloses a three-piece solid golf ball having an ionomer cover and a solid core consisting of a soft inner core and a hard outer shell, where the difference in the hardness of the two parts of the core is at least 10 on the JIS-C scale.
Similarly, U.S. Pat. No. 4,781,383 discloses a solid, three-piece golf ball, having an ionomer cover and a core with inner and outer layers, where the inner layer has a diameter of 24 to 29 mm and a Shore D hardness of 15 to 30, and the outer layer has a diameter of 36 to 41 mm and a Shore D hardness of 55 to 65.
European Patent Application 0 633 043 discloses a solid, three-piece golf ball with an ionomer or balata cover, a center core, and an intermediate layer. The center core has a diameter of at least 29 mm and a specific gravity of less than 1.4. The intermediate layer has a thickness of at least 1 mm, a specific gravity of less than 1.2, and a hardness of at least 85 on the JIS-C scale.
U.S. Pat. No. 5,688,192, to Aoyama, discloses compressible materials, i.e., gases, in the core of a solid construction golf ball to simulate the effects of trapped air in a wound ball.
None of these disclosures utilizes the unique physical properties of liquid crystalline polymeric materials, and there is no known disclosure of a golf ball using these materials.
Liquid crystalline polymers exhibit unique properties due to anisotropic ordering and orientation of the polymer chains within macroscopic domains of the material. The domain ordering in liquid crystalline polymers is typically dependant on the conditions under which the polymers are processed, and the ordering may be obtained either by varying the concentration of the polymer in solution ("lyotropic" liquid crystallinity) or by varying the temperature of the neat polymer ("thermotropic" liquid crystallinity). For thermotropic liquid crystalline polymers, the domain ordering is maintained at temperatures at which the materials are fluid; such ordered fluid phases are termed "mesophases" in that their characteristics are intermediate between those of an isotropic liquid and those of a crystalline solid.
As illustrated in FIG. 4, there are three common mesophase structures of thermotropic liquid crystalline polymers: 1) nematic mesophase structures in which the polymer chains on average are parallel to one another but there is no other structural ordering; 2) smectic C mesophase structures in which the polymer chains (or blocks within the polymer chains) are parallel to one another and also form a layered structure, with the parallel direction of the polymer chains (or blocks within the polymer chains) being other than perpendicular to the planes of the layers; and 3) smectic A mesophase structures in which the polymer chains (or blocks within the polymer chains) are parallel to one another and also form a layered structure, with the parallel direction of the polymer chains (or blocks within the polymer chains) being perpendicular to planes of the layers.
Domain ordering makes certain liquid crystalline polymers extremely durable. It makes other liquid crystalline polymers particularly elastic, or thixotropic, or compressible. Furthermore, polymer blends that include liquid crystalline polymers have been found to be self-reinforcing.
Self-reinforcing blends, also known as microcomposites, form when one or more liquid crystalline polymers are blended with one or more thermoset or thermoplastic polymers in such a way that the liquid crystalline polymer or polymers form fibrillar domains within the blend. These fibrillar domains act to reinforce the overall blend in much the same fashion as with steel rods ("re-bar") in a concrete fabrication. The self-reinforcing blends can be designed to produce mechanical properties intermediate between those of the liquid crystalline polymer or polymers and those of the thermoset or thermoplastic polymer or polymers.
Thermotropic liquid crystalline polymers have recently become commercially available. For example, Hoechst Celanese produces and markets Vectra.RTM., and Amoco Manufacturing produces and sells Xydar.RTM..
Thermotropic liquid crystalline polymers attain their ordering due to mesogenic units that are part of the polymer macromolecules. These mesogenic units are typically, though not exclusively, comprised of functionalized and non-functionalized, polarizable, aromatic and heteroaromatic groups; and these mesogenic units may be accompanied by less polarizable aliphatic groups that act as spacer units in the polymers. Thermotropic liquid crystalline polymers may be divided into two broad categories, main chain and side chain liquid crystalline polymers, that differ according to whether the mesogenic units are part of the polymer backbone (main chain) or are appended to the polymer backbone (side chain).
Thermotropic liquid crystalline polymers are well known. For example, U.S. Pat. Nos. 5,334,695 and 4,963,642, both to Roggero et al., disclose thermotropic copolyesters containing (I) spacer units derived from a saturated, aliphatic dicarboxylic acid, and (II) mesogenic units derived from combinations of (a) 4,4'dihydroxybiphenyl and alkyl or alkenyl derivatives of 4,4'dihydroxybiphenyl, and (b) 4-hydroxybenzoic acid or alkyl and alkenyl derivatives of 4-hydroxybenzoic acid.
Other examples of thermotropic liquid crystalline polymers are found in U.S. Pat. No. 5,298,593 to Fujiwara et al., which discloses polyesters produced by polycondensation of an ester monomer of the formula R.sup.2 --COO--Ar.sup.1 --COO--R.sup.1 --OOC--Ar.sup.1 --OOC--R.sup.2 with an aromatic dicarboxylic acid compound of formula X.sup.1 --OOC--Ar.sup.2 --COO--X.sup.2 and aromatic carboxylic acid compound of formula R.sup.3 --OOC--Ar.sup.2 --X.sup.3, where R.sup.1, R.sup.2, and R.sup.3 are independently 1 to 6 carbon alkyl or alkenyl groups, Ar.sup.1, Ar.sup.2, and Ar.sup.3 are independently substituted or unsubstituted 6 carbon to 18 carbon aromatic hydrocarbons, and X.sup.1, X.sup.2, and X.sup.3 are independently either hydrogen or 1 to 10 carbon alkyl groups.
U.S. Pat. No. 5,034,540 to Haitko et al. discloses thermotropic liquid crystalline polymers comprising polyesteretherimide repeating units of the structure --O--Ar-PABA-o-phthalimide- where PABA has the usual meaning of p-aminobenzoic acid, and Ar signifies p-phenyl, 4,4'-biphenyl, or 2,6-naphthyl subunits.
U.S. Pat. No. 4,970,286 to Gentz et al. discloses fully aromatic moldable liquid crystalline polyesters that are melt processible at relatively low temperatures, and whose mesogenic units include 4,4"-terphenyldicarboxylic esters, p-hydroxybenzoic esters, terephthalic esters, hydroquinone esters, and combinations of these esters.
Davies and Ward, in High Modulus Polymers, Zachariades, A. and Porter, R, Eds., Marcel Dekker, N.Y., 1987, Ch. 2, disclose liquid crystalline copolyesters of p-hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid.
Jackson and Morris, in Liquid Crystalline Polymers (ACS Symposium Series 435) R. A. Weiss and C. K. Ober, Eds., American Chemical Society, Washington, D.C., 1990, Ch. 2, disclose liquid crystalline homo and copolyesters of 4,4'-biphenyl-dicarboxylic acid and trans-4,4'-stilbene-dicarboxylic acid.
Lewis and Fellers, in High Modulus Polymers, Zachariades, A. and Porter, R, Eds., Marcel Dekker, N.Y., 1987, Ch. 1, disclose processing of liquid crystalline homo- and co-polyesters of hydroquinone terephthalate, p-acetoxybenzoic acid, 2,6-dihydroxynaphthalene, and 2,6-naphthalenedicarboxylic acid.
None of these references teach the use of liquid crystalline polymers in the golf ball art.
Liquid crystalline polymers and polymer blends, which can be thermoformed, provide their desired physical properties with the fabrication ease of polyethylene, making them particularly suitable for use in golf balls.
Blends of liquid crystalline polymers with other liquid crystalline and thermoset or thermoplastic materials are also known. For example, U.S. Pat. No. 5,545,686, to Carter, discloses rubber compositions that are blends of one or more elastomers with one or more thermotropic liquid crystalline polymers and carbon black.
Another example of a thermoformable blend is found in U.S. Pat. No. 5,346,970 to Dashevsky et al., which discloses moldable blends of flexible coil polymers such as poly(ethylene terephthalate) ("PET") with liquid crystalline polymers and liquid crystalline block copolymers of the formula ----O-p-Phenyl-COO--(CH.sub.2).sub.n -p-Phenyl -CO--!.sub.x --where n is between 2 and 10 and x is between 2 and about 50.
Another blend comprising a liquid crystalline polymer is found in U.S. Pat. No. 5,011,884 to Roseneau et al., which discloses molding compositions formed from blends of thermotropic liquid crystalline polymers with polyesters and polycarbonates.
Blends between thermotropic liquid crystalline polymers and linear alternating polymers formed between carbon monoxide and ethylenically unsaturated hydrocarbons are disclosed in United States Statutory Invention Registration H1187 to George et al.
Blends of liquid crystalline polymers with thermoplastic elastomers are also known. For example, in Polym. Eng. Sci. 36, (1996) 2451, Machiels and coworkers disclose the preparation and properties of in situ composites based on Vectra.RTM. A900 (a liquid crystalline random copolyester of about 73 wt. % 4-hydroxybenzoic acid and 27% 2-hydroxy-6-naphthoic acid) and Arnitel.RTM. em630 elastomer (a block copolymer comprising a blend of about 25 wt. % poly-oxytetramethylene with about 75 wt. % polybutylene terephthalate). Such composites show significant increase in storage moduli and tensile strengths as compared to the unblended elastomers.
Processing conditions and blends between thermotropic liquid crystalline polymers and melt-processible thermoset or thermoplastic polymers, which blends exhibit improved properties over conventional polymers, are disclosed in UK Patent Application GB 2288176 A to Makhija et al.
Blends between main chain and side chain liquid crystalline polymers are found in U.S. Pat. Nos. 4,842,754 and 4,952,334, both to Hakemi et al., which disclose compatible blends of at least one main chain thermotropic liquid crystalline polymer with at least one side chain liquid crystalline polymer, both polymers comprising mesogenic units connected by ester, amide, imide, keto and ether linkages, and both polymers comprising a wide variety of aromatic and heteroaromatic mesogen units, and both polymers optionally containing spacer units.
Self-reinforcing blends of at least two liquid crystalline polymers are found in U.S. Pat. No. 5,070,157, to Isayev et al., which discloses blends of wholly aromatic polyesters that phase-separate in the solid state due to high-strain melt processing.
Foamable liquid crystalline polymers are also known. For example, U.S. Pat. Nos. 4,429,060 and 4,429,061, both to Ide, disclose high performance foams of thermotropic liquid crystalline polymers. The polymers disclosed include esters of 6-hydroxy-2-naphthoic acid, meta- and para-hydroxy benzoic acids, terephthalic acid, and combinations of these acids.
Liquid crystalline elastomers are also well known. For example, Rudolf Zentel and coworkers have published a series of papers describing both main chain and side chain liquid crystalline polyacrylates, as well as side chain liquid crystalline polysiloxanes.
In Angew. Chem. Adv. Mater. 101, (1989) 1439, Zentel discloses main chain elastomeric liquid crystalline 6-{4-4'-(6-hydroxy-1-hexoxy)phenyl!-phenoxy}-1-hexyl 2-prop-2-enyl) malonic polyesters that are crosslinked using siloxane oligomers. In that paper, Zentel also discloses side chain polyacrylic and polymethylmethacrylic liquid crystalline polymers where the pendant mesogenic ester is a 6-{4-4'-methoxy) phenoxy-carbonyl!phenoxy}-1-hexyl group and there is a minor fraction of .omega.-hydroxyhexyl pendant ester groups that are crosslinked using bis-4-isocyanatophenyl methane.
In Makromol. Chem. 188, (1987), 665, Zentel and Benalia disclose side chain polyacrylic liquid crystalline polymers where the pendant mesogenic ester is a 6-{4-4'-cyano) phenoxycarbonyl!phenoxy}-1-hexyl group, and there minor fraction of .omega.-hydroxy-n-hexyl ester groups that are crosslinked using 1,6-diiso-cyanatohexane.
In Chemtech, May 1995, 41, Zentel and Brehmer disclose liquid crystalline polysiloxane elastomers formed by reaction of a polysiloxane with 4'-acetoxy-4-undec-1-en-11-oxy!-biphenyl followed by functionalization with N-(5-carboxypentyl) acrylamide and photolytic crosslinking.
Other liquid crystalline elastomers are disclosed by Finkelman and coworkers. For example, in Makromol. Chem. 188, (1987), 1489, Gleim and Finkelman disclose liquid crystalline polysiloxane elastomers formed by reaction of a polysiloxane with 4'-methoxyphenyl-4-.omega.-vinyl-n-butoxy) benzoate and with 4'-methoxyphenyl-4-.omega.-vinyl-n-pentoxy) benzoate; these elastomers are crosslinked using .alpha.-.omega.-divinyl siloxane oligomers.
Finally, Davis et al. disclose liquid crystalline crosslinked elastomers formed by copolymerization of ethylene glycol diacrylic ester and 2-4-(4'-cyanophenoxycarbonyl)-phenoxy!ethyl acrylate.
Liquid crystalline ionomers are also known. For example, in J. Polym. Sci; Pt. A: Polymer Chemistry, 30, (1992) 91, Zhang et al. disclose main chain liquid crystalline ionomers formed from copolymerization of a dye, brilliant yellow, with 4,4'-dihydroxy-.alpha.,.alpha.'-dimethyl-benzalazine and either dodecanedioyl chloride or sebacoyl chloride to form their respective ester spacer groups.
Injection molding of thermotropic liquid crystalline polymers and polymer blends is well known. For example, U.S. Pat. No. 4,627,952 to Ophir describes an apparatus and process for maintaining laminar flow during the entire injection process of thermotropic liquid crystalline polymers.
Handlos and Baird in International Polymer Processing, (1996) 82, describe a process for preforming pellets of a liquid crystalline and thermoset or thermoplastic polymer blend, where such pellets are then used as feed stock for injection molding of such blends, and where the so molded blend forms a self-reinforcing composite.
Lekakou et al., in J. Mater. Sci., 32 (1997) 1319, describes how to improve the self-reinforcement of injection-molded liquid crystalline polymers.
Lewis and Fellers, in High Modulus Polymers, Zachariades, A. and Porter, R, Eds., Marcel Dekker, N.Y., 1987, Ch. 1, discuss a wide variety of liquid crystalline polymers and polymer blends that are processible by injection molding.
O'Donnell et al., in ANTEC '94, (1994) 1606, describes injection molding techniques for composites between polypropylene and liquid crystalline polymers.
Xu et al., in Polym. Eng. Sci., 36 (1996) 769, describes injection molding of a ternary blend of a liquid crystalline polymer with polybutylene terephthalate and polycarbonate. This ternary blend exhibits improved mechanical properties over binary blends involving liquid crystalline polymers.
None of these references discloses the use of liquid crystalline polymers in the golf ball art. Therefore, there is a need in the golf ball art for a golf ball incorporating liquid crystalline polymers and blends of liquid crystalline polymers and other polymers. As described below, the inclusion of foamed and unfoamed liquid crystalline polymers and liquid crystalline polymer blends will allow highly durable golf balls to be produced with virtually any combination of feel and spin rate.